Beverages such as soft drinks, beer, tea, juice, water, and concentrate are commonly sold in metal cans. A typical can includes a bottom wall having an inwardly disposed concave dome shape, and a cylindrical sidewall extending from the bottom wall and terminating in a necked end to which a can end is secured. The end includes a score line and a stay-on-tab attached by a rivet outside the score line.
The sidewalls of these metal can bodies are typically formed by a drawing and ironing (D&I) process. In the beer and beverage industry, the cans have a nominal can diameter of, for example, two and eleven sixteenths inches (a "211 can") and, after being filled with beverage, the open end is sealed with the can end. Prior to filling, the open end is necked in, for example, to a neck diameter of 206 (two and six sixteenths inches) on the standard 211 can or possibly to a 204 neck (two and four sixteenths) or a 202 neck. Typical processes for necking cans are disclosed in U.S. Pat. No. 5,297,414 to Sainz (die necking) and U.S. Pat. No. 5,245,848 to Myrick et al (spin flow necking).
Typically, the exterior surface of the can sidewall is printed with advertising and other information. The interior surface has a clear coating that prevents the can contents from chemically interacting with the metal sidewalls.
Selected areas of the exterior wall may also be mechanically deformed in various ways to enhance their appearance. It is known to form or shape cans by embossing the sidewalls of such cans in various aesthetically appealing patterns which may comprise marks or outlines associated with a particular beverage and company, as disclosed for example in U.S. Pat. No. 3,628,451 to McClellan et al., entitled "Apparatus For and Method Of Shaping Workpieces".
An alternative method for expanding the sidewall of a can using EM forces is disclosed in U.S. Pat. No. 4,947,667 to Gunkel et al., entitled "Method and Apparatus For Forming a Container." In EM forming, a magnetic field of relatively high intensity is formed by passing an electric current through a constant diameter coil consisting of a conductive wire which is typically supported by a nonconductive structure. The coil is inserted into the constant diameter can interior through the open end in close, yet radially spaced proximity to the can sidewall. The current produces a pulsed magnetic field which induces a current in the adjacent conductive can. The induced current in the workpiece reacts with the magnetic field to produce a force which is directed against the adjacent can sidewall, deforming it radially outward, preferably into a mold including a contoured inner cavity.
Contouring the sidewall reduces the column strength of the can, which may make some necking processes, for example die necking, unsuitable if necking is performed after EM contouring. On the other hand, reversing the order of the steps and performing necking before EM contouring by prior art processes is also undesirable, since it may be impossible for the diameter of the EM coil to be small enough to allow the coil to fit through the neck, yet large enough to position the coil sufficiently close to the can sidewall for the EM forces to do their job efficiently and effectively.